DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a fixing device for use in an image recording apparatus of the electrophotographic type such as an electronic copying machine or a facsimile.
2. Prior Art
Conventionally, in an image recording apparatus of the electrophotographic type such as an electronic copying machine or a facsimile, there is widely used a fixing device in which a sheet having a toner image transferred thereto is passed through a nip portion between a pair of rollers consisting of a fixing roller and a compression roller to thereby fuse the toner image to the sheet by means of heating by the fixing roller and compression by the two rollers.
Generally, in this fixing method, since the toner image fused to the sheet comes into contact with the fixing roller, a roller having a fluorine resin coating layer with high mold release characteristics is used. However, even if such a fixing roller is used, the fused toner easily adheres to the surface of the fixing roller because it is soft and highly viscous, and the sheet may wind around the fixing roller. Thus, there is normally adopted a method to prevent the sheet from winding around the fixing roller with the provision of a forced peeling device using such a peeling claw as described below.
FIG. 10 is a schematic structural view showing a conventional fixing device having a forced peeling device using a peeling claw.
As shown in FIG. 10, this fixing device comprises: a fixing roller 1 incorporating a heater 2 therein, which rotates in a direction indicated by an arrow A; a compression roller 6, which rotates in a direction indicated by an arrow B in contact with the fixing roller 1; and a peeling claw 10, whose end edge comes into contact with the surface of the fixing roller 1 to peel a sheet P, which has passed through a nip portion N, away from the fixing roller 1, provided downstream of the nip portion N where the fixing roller 1 and the compression roller 6 contact one another with respect to the direction of rotation of the fixing roller 1. As the compression roller 6, a rubber roller is normally used, and is arranged so as to press against the fixing roller 1 at predetermined pressure.
As the peeling claw 10, there has conventionally been used a peeling claw obtained by molding heat-resistant resin such as polyimide and polyphenylene sulfite and finishing its tip end into a sharp shape. Such a peeling claw 10 is arranged such that it is pressed against the surface of the fixing roller 1 using a spring. The width of the end edge of the peeling claw 10, which comes into contact with the surface of the fixing roller 1, is nearly 2 mm, and a plurality of the peeling claws 10 with narrow widths are normally arranged in the axial direction of the fixing roller 1. Since the peeling claws 10 only partially come into contact with the surface of the fixing roller 1 in this way, uneven pressure due to the peeling claws 10 is applied onto the surface of the fixing roller 1 in the axial direction thereof, and as a result, the surface may be partially worn or scratched. Also, in a case where the sheet hooks on any one of the plurality of peeling claws to cause winding of the sheet, the adjacent peeling claws may receive an unusual force caused by the sheet to be strongly pressed against the fixing roller 1, or to be deformed, thus seriously scratching the surface of the fixing roller 1 or causing partial wear.
In order to solve such problems, there is disclosed in Japanese Published Unexamined Patent Application No. Sho 59-188681 a fixing device for peeling a sheet by means of the following plastic peeling sheet.
FIG. 11 is a schematic structural view showing a conventional fixing device having a forced peeling device using a plastic peeling sheet.
As shown in FIG. 11, this fixing device comprises: a fixing roller 1 incorporating a heater 2, which rotates in a direction indicated by an arrow A; a compression roller 6, which rotates in a direction indicated by an arrow B in contact with the fixing roller 1; and a peeling sheet 11, whose end edge comes into contact with the surface of the fixing roller 1 to peel a sheet P, which has passed through a nip portion N, away from the fixing roller 1, provided downstream of the nip portion N where the fixing roller 1 and the compression roller 6 contact one another with respect to the direction of rotation of the fixing roller 1. For the peeling sheet 11, there is used a plastic sheet having a thickness of 0.05 mm or more, flexural modulus of elasticity of 10.sup.3 kg/cm.sup.2 or more and a melting point of 150.degree. C. or higher, and it is arranged so that its sharp end edge comes into uniform contact with the entire surface of the fixing roller 1 in the axial direction therefor.